(1.) Field of the Invention
This invention refers to an electronic component such as an inductor, a bandpass filter, or a duplexer, and its production method. In the above product, a non-metal core layer has conductive lands formed on one or both surfaces thereof, and the obtained item is shielded.
(2.) Description of the Prior Art
A conventional bandpass filter will be explained as an example of the prior art. FIG. 1 shows a front view of a bandpass filter, FIG. 2 a bottom view of the same, and FIG. 3 a rear view of the same.
As shown in FIGS. 1, 2 and 3, a dielectric layer 220 has substantially C-shaped conductive lands 221 and 222 symmetrically arranged on its upper surface and substantially C-shaped conductive lands 223 and 224 symmetrically arranged on its bottom surface. The conductive lands 221 and 222 are soldered with grounding terminals 225, and the conductive lands 223 and 224 are soldered with external lead terminals 226. Such a bandpass filter is molded and shielded in the following manner.
The whole part of the bandpass filter, excluding the projecting portions of the grounding terminals 225 and the external lead terminals 226, is immersed in an insulating resin bath, whereby the bandpass filter is wrapped up by a resin film (not shown). The obtained item is further wrapped up with a magnetic substance (not shown).
Such a shielding method prevents the frequency characteristic of the bandpass filter from declining even if it is approached by a metal or other conductors. This shielding method is employed for other electronic components as well as for a bandpass filter.
When the above shielding method is applied, however, magnetic permeability of the shielding magnetic substance varies in accordance with the frequency characteristic. In consequence, the magnetic permeability drops in a high frequency range to the level where the shielding effect is not enough.
Furthermore, the above production method requires many processes such as core layer baking, conductive lands forming, terminal soldering, immersing and shielding.
In recent years, another production method has been proposed, where shielding electrodes are incorporated in the bandpass filter, and the obtained item is baked. By this method, baking does not have to be done as many as times by the above conventional method. However, this proposed method has a problem that the bandpass filter core inside the shielding electrodes declines its Q factor to have low quality.